1. Field of the Invention
The present invention relates to a new method for synthesizing crystalline molecular sieves using a new family of templating agents.
2. Background
The crystalline materials of this invention contain metallic and non-metallic oxides bonded through oxygen linkages to form a three-dimensional structure. Molecular sieves are a commercially important class of crystalline materials. Natural and synthetic crystalline molecular sieves are useful as catalysts and adsorbents. They have distinct crystal structures with ordered pore structures which are demonstrated by distinct X-ray diffraction patterns. The crystal structure defines cavities and pores which are characteristic of the different species. The adsorptive and catalytic properties of each molecular sieve are determined in part by the dimensions of its pores and cavities. Thus, the utility of a particular molecular sieve in a particular application depends at least partly on its crystal structure.
The term "molecular sieve" refers to a material prepared according to the present invention having a fixed, open-network structure, usually crystalline, that may be used to separate hydrocarbons or other mixtures by selective occlusion of one or more of the constituents, or may be used as a catalyst in a catalytic conversion process.
The term "zeolite" refers to a molecular sieve containing a silicate lattice, usually in association with some alumina, boron, gallium, iron, and/or titanium. In the following discussion, the terms molecular sieve and zeolite will be used more or less interchangeably, since most of the work was carried out on zeolites. However, one skilled in the art will recognize that the teachings relating to zeolites are also applicable to the more general class of materials called molecular sieves.
The term "aluminosilicate" refers to a zeolite containing both framework alumina and framework silica. The term "silicate" refers to a zeolite having a high SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio, preferably a SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio greater than 100. The term "borosilicate" refers to a zeolite containing both boron and silicon, and having a SiO.sub.2 /B.sub.2 O.sub.3 ratio of greater than 20.
Organic templating agents are believed to play an important role in the process of molecular sieve crystallization. Organic amines and quaternary ammonium cations were first used in the synthesis of zeolites in the early 1960's. This approach led to a significant increase in the number of new zeolitic structures discovered as well as an expansion in the boundaries of composition of the resultant crystalline products. Previously, products with low silica to alumina ratios (SiO.sub.2 /Al.sub.2 O.sub.3 .ltoreq.10) had been obtained, but upon using the organocations as components in the starting gels, zeolites with increasingly high SiO.sub.2 /Al.sub.2 O.sub.3 ratios were realized.
Crystalline aluminosilicates are usually prepared from aqueous reaction mixtures containing alkali or alkaline earth metal oxides, silica, and alumina. By varying the synthesis conditions and the composition of the reaction mixture, different zeolites can be formed using the same templating agent.
Compounds having chemical structures which fall outside the scope of the present invention have also been disclosed as templating agents for various crystalline materials. Use of N,N,N-trimethyl cyclopentylammonium iodide in the preparation of Zeolite SSZ-15 molecular sieve is disclosed in U.S. Pat. No. 4,610,854; use of 1-azoniaspiro [4.4] nonyl bromide and preparation of a molecular sieve termed "Losod" is disclosed in Hel. Chim. Acta (1974), Vol. 57, page 1533 (W. Sieber and W. M. Meier); use of 1,.omega.-di(1-azoniabicyclo [2.2.2.] octane) lower alkyl compounds in the preparation of Zeolite SSZ-16 molecular sieve is disclosed in U.S. Pat. No. 4,508,837; use of N,N,N-trialkyl-1 adamantammonium salts in the preparation of zeolite SSZ-13 molecular sieve is disclosed in U.S. Pat. No. 4,544,538. U.S. Pat. No. 5,053,373 discloses preparing SSZ-32 with an N-lower alkyl-N'-isopropyl-imidazolium cation templating agent. U.S. Pat. No. 5,106,801 discloses a cyclic quaternary ammonium ion, and specifically a tricyclodecane quaternary ammonium ion, for the preparation of the metallosilicate zeolite SSZ-31. U.S. Pat. No. 4,910,006 teaches using a hexamethyl[4.3.3.0] propellane-8,11-diammonium cation for the preparation of SSZ-26. EP 0193282 discloses a tropinium cation for preparing the clathrasil ZSM-S8. Similarly, use of quinuclidinium compounds to prepare a zeolite termed "NU-3" is disclosed in European Patent Publication No. 40016. Use of aza-polycyclic templates to prepare molecular sieves is disclosed in copending U.S. Pat. Application No. 907,419, filed Jun. 30, 1992, entitled "METHOD FOR PREPARING. CRYSTALLINE MATERIALS USING AZA-POLYCYCLIC TEMPLATING AGENTS."